Power transmission



Oct l940- F. T. HARRINGTON ET'AI. I 2,219,896

I POWER TRANSMISSION I Q Filed July 17, 1939 INVENTORS FERRIS "r. HARRINGTON a RALPH 1.. TWEEDALE I 5 ATTORNEY Patented Oct. 29, 1940 UNITED STATES PATENT OFFICE POWER TRANSMISSION Application July 17, 1939, Serial No. 284,913 6 Claims. (01. 60-52) This invention relates to power transmissions and particularly to those of the type comprising two or more fluid pressure energy translating devices, one of which may function as a pump and 5 another as a motor.

The invention is more particularly concerned with a hydraulic transmission system for operating a hydraulic press or analogous device.

Presses of this character are frequently provided with a surge tank at the top of the press and with the hydraulic control mechanism and pump also mounted at the top of the press either in or adjacent to the surge tank. In very large presses the necessary manual controls must be 1 located within reach of the operator near the bottom of the press, and it has 'been common practice to provide an electric circuit for operating the control mechanism at the surge tank by means of push button switches located within 20 reach of the operator at the bottom of the press and arranged to selectively energize solenoids which are connected to operate the hydraulic controls overhead.

It is also desirable in many press installations 25 to provide for reversing the press platen when the operating pressure in the main cylinder reaches a predetermined peak value. In presses of this character a commonly used expedient is to provide a solenoid for pulling the hydraulic 30 control member into pressing position which solenoid is energized by a momentary-contact, normally-open, push button switch and to provide a holding relay for the solenoid, the holding circuit of which is arranged to be opened by a 35 pressure responsive electric switch when the main ram pressure builds up to the desired peak. The control operating solenoid is thus deenergized permitting a spring or other biasing means to throw the control over to platen reversing posi- 40 tion. Usually a mechanical or other connection between the platen and the control is provided for shifting the control member to neutral position when the platen is fully returned.

Control circuits of this character have pre- 45 sented certain difiiculties arising at the time of reversal of the press. If the hydraulic control member happens to be a four-way valve, the sudden shifting of the same from its pressing position to its platen returning position at the 50 time when the pressure switch opens the holding circuit causes a sudden release of the extremely large amount of energy which is stored in the main cylinder and causes deleterious shocks of great magnitude. One object of the present 55 invention is to provide a hydraulic power transmission system for operating a hydraulic press wherein these difliculties are avoided.

These and other objects areaccomplished by the provision of a four-way valve which is spring biased to neutral position in which the main 5 cylinder is exhausted to tank along with the pump delivery line. Separate electric means are provided for shifting the valve to its pressing position and to its platen returning position together with an electric control circuit including a pressure responsive switch arranged to control initiation of both the electric valve operating means. The construction of the pressure switch and the arrangement of the circuit is such that at the time of reversal the valve is permitted to come to central position momentarily and is prevented from shifting to reverse position until the main cylinder pressure has fallen substantially to zero.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing wherein a preferred form of the present invention is clearly shown.

In the drawing:

The single figure is a diagrammatic view of a power transmission system embodying a preferredform of the present invention.

A pump l0 may be driven by a suitable prime mover, such as an electric motor l2, and has a suction conduit It for withdrawing fluid from a tank l6 and a delivery conduit iii in which is incorporated a customary relief valve 2t.

The conduit I8 connects to a pressure port 22 of a spring-centered, solenoid-operated, fourway valve 24. The latter has cylinder ports 26 and 28 and tank ports 30 and 32. The latter are connected with the tank l6 by a conduit 34. The valve has a spool 36 provided with a blocking land 38 registering with the port 28 in neutral position 40 and with a cut-away land 40 registering with the port 26 in neutral position. Suitable springcentering means at 42 are provided for normally retaining the spool in the central position illustrated. Push-type solenoids and 46 are provided for shifting the spool to the right and left respectively from the central position illustrated.

A conduit 48 connects the cylinder port 26 with the main cylinder 50 of a hydraulic press and also with the head end of booster cylinders 52. 50 A conduit 54 connects the cylinder port 28 with the rod end of the cylinders 52 which serve as pull-backs. The press platen is indicated diagrammatically at 58 and carries the main ram 58 slidable in the cylinder 50 as well as the rods 55 88 of pistons 88 slidable in the cylinders 82. The parts thus far described constitute the basic elements of a typical hydraulic press-operating circult and are intended as a diagrammatic showing only, it being understood that the circuit is capable of many variations and refinements as is well known in the art.

Connected to the main cylinder line 88 by a branch conduit 82 is a pressure responsive switch 88. The latter is provided with a switch-operating cylinder 88 in which is mounted a small ram 88 biased to the right by a spring I0 which is positioned in a seepage drain chamber I2. The latter is connected to tank by a conduit I8.

The conduit 82 leads through a restriction I8 to a spring-loaded ball valve I8 adapted to remain closed until a predetermined pressure is reached which may be made to take place at any value desired by adjustment of a spring abutment screw 88.. The outlet side of valve I8 connects with the chamber 88 by a conduit 82. Arranged in parallel with the valve I8 between chamber 88 and restriction I8 is a check valve 88 arranged to permit free flow from chamber 88 to conduit 82 but to prevent flow therethrough v in the opposite direction.

The ram 88 when shifted to the left abuts .against an operating stem 88 of a two-circuit,

normally-closed switch 88. The switch 88 normally connects conductors 88 and 82 with one side of a suitable power supply line indicated at L Conductor 88 extends to a normally-closed push-button switch 88 from which a conductor 88 extends to one circuit of a holding relay 88. From the relay 88 a conductor I00 extends to the solenoid 88 and thence to the other side of the line L. The operating coil I02 of relay 88 is connected by a conductor I88 with a normallyopen, push-button switch I88 which is connected by a conductor I08 with the conductor 80. The coil I02 also connects to the holding contacts of the relay 88 by a conductor IIO, the other side.

of the holding contacts being connected by a conductor II2 with the conductor 88.

The conductor 82 extends to the other circuit of relay 88 from which a conductor II8 extends to the solenoid 88 which is also connected to line IF. The relay 88 has an, operating stem II8 which is normally biased upwardly by a spring II8. A lever I20 pivoted to a stationary part of the press at I22 has its left end contacting the stem H8 and its right end arranged in the path of travel of a dog I28 carried by the platen 58. Thus whenever the platen reaches its upper limit of movement, the lever I20 is swung counterclockwise to depress the stem II8 into the position illustrated in the drawing.

In operation, with the parts in the position shown and with the motor I2 driving the pump I0, oil is withdrawn from the tank through suction conduit I8 and delivered through conduit I8 to the port 22 of valve 28. The full pump delivery is by-passed to tank by passing across the cut-away land to the port 80 and through conduit 88. The platen is prevented from falling by the fluid trapped in the rod ends of the cylinders 52 which cannot escape from the conduit 58 through port 28due to the blocking land 88 of spool 88.

when it is desired to initiate a single cycle of press operation, the switch I08 is depressed permitting current to flow from line L through switch 88, conductor 80, conductor I08, switch I08, and conductor I88 to the operating coil I02. The stem I I8 is accordingly pulled downwardly establishing the holding circuit which extends through switch 88. conductor 88, switch 88, conductors 88 and H2, and conductor I It to the coil I82. The relay 88 accordingly remains down without requiring further holding of the switch I88 closed.

With the relay 88 down. the solenoid 88 is energized through'switch 88, conductor 80, switch 88, conductor 88, relay 88, and conductor I00. Spool 88 is accordingly shifted to the left against its spring bias and remains in this position so long as solenoid 88 remains energized. In this position the pump delivery is directed from port 22 to port 28 and through conduit 88 to the main cylinder 88 and to the head end of booster cylinders 82. The platen accordingly descends, forcing oil from the rod ends of cylinders 82 through conduit 88 and port 28 which is now connected to port 82 from which the discharge continues to tank through conduit 88.

As the platen meets the work and completes the pressing stroke, the pressure in line 88 builds up until it reaches a value such that the springloaded valve 18 will open admitting oil to chamber 88 through conduit 82. At this point the small ram 88 is pushed fully to the left opening both circuits of switch 88 and thereby deenergizing solenoid 88 and the operating coil I82 of relay 88.

Since the platen is now in its down position, the lever I20 does not interfere with upward movement of the stem II8 which is shifted upwardly by spring II8 to close the circuit between conductors 92 and H8. At this moment, however, this circuit is incomplete at the switch 88. Accordingly both solenoids 88 and 88 are deenergized momentarily permitting the spool 88 to come to center position under the action of springs 82, thus connecting the main cylinder line 88 to tank across the cut-away land 80.

The potential energy stored in the compressed oil and in the highly stressed tension rods of the press is thus permitted to escape. Until this energy does escape and the pressure in line 88 falls substantially to zero, the oil in chamber 88 is trapped and the ram 88 remains in its left-hand position. As soon as this pressure is relieved, however, the spring 10 is able to force the ram 88 back to the right, discharging oil from chamber 88 through check valve 88, conduits 82 and 88, ports 28 and 80, and conduit 88 to tank. The switch 88 accordingly again closes at this point completing the circuit to solenoid 88 through line L switch 88, conductor 92, relay 88, and conductor H8. The spool 36 is accordingly shifted to the right connecting the pump delivery through ports 22 and 28 and conduit 58 to the rod ends of cylinders 82. The platen is accordingly moved upwardly, discharging oil from the head ends of cylinders 52 and from the main cylinder 50 through conduit 88, ports 28 and 30, and conduit 88 to tank.

As soon as the platen approaches the upper limit of its stroke, the dog I28 shifts the lever I20 counterclockwise, depressing the stem II8 of relay 88 to open the circuit 92-I I8, thus deenergizing solenoid 88. The spool 88 accordingly shifts to center position under the action of springs 82 thus restoring the parts to the position from which they started.

If at any time during pressing stroke it should be necessary to reverse the press manually, this may be done by depressing the switch 88 which deenergizes the solenoid 88 and also the operating coil I02 of relay 88. Since the switch 88 remains closed at this time, the solenoid 44 will be immediately energized causing the platen to return in the manner previously described. In thus reversing the press in an emergency the valve spool 36 is shifted substantially instantaneously without hesitation into reversing position, which is permissible since the main ram pressure is not high,

and there is accordingly no appreciable potential energy stored in the compressed oil and the stressed rods of the press.

It will be understood that the advantages of the present invention may be derived from many various circuit arrangements including those wherein reversal of the press is made to take place in response to the platen reaching a predetermined position. Thus the conductor 90 may be controlled by a limit switch operated by the platen instead of by the pressure switch 64 which, however, may be utilized for control of the circuit 92 in the manner described.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. In a hydraulic power transmission system for operating a press or the like the combination with a source of pressure fluid and a reversible fluid motor of a valve shiftable to forward and reverse positions to direct fluid to the motor in either direction and having a neutral position in which fluid is exhausted from one side of the motor, an electric operator for shifting said valve to forward position, an electric operator for shifting the valve to reverse position, means normally biasing the valve to neutral position, means for initially energizing the first electric operator, and means responsive to a predetermined rise in motor pressure for deenergizing the first operator to permit the valve to shift to neutral position under its bias for exhausting pressure fluid from the motor and thereafter responsive to a predetermined fall in motor pressure for energizing the second operator.

2. In a hydraulic power transmission system for operating a press or the like the combination with a source of pressure fluid and a reversible fluid motor of a valve shiftable to forward and reverse positions to direct fluid to the motor in either direction and having a neutral position in which fluid is exhausted from one side of the motor, electric operating means for shifting the valve, and a control circuit including switch means responsive to a predetermined pressure rise at said one side of the motor for causing shifting of the valve first to neutral position and thereafter responsive to a predetermined pressure fall at said one side of the motor for then causing shifting of the valve to reverse position.

3. In a hydraulic power transmission system for operating a press or the like the combination with a source of pressure fluid and a reversible fluid motor of a valve shiftable to forward and reverse positions to direct fluid to the motor in either direction and having a neutral position in which fluid is exhausted from one side of the motor, an electric operator for shifting said valve to forward position, an electric operator for shifting the valve to reverse position, means normally biasing the valve to neutral position, means for initially energizing the first electric operator, and a single pressure responsive switch for controlling the deenergization of the first operator in response to a predetermined rise in pressure at said one side of the motor and arranged to control the energization of the second operator in response to a predetermined fall in pressure at said one side of the .motor thereafter.

4. In a hydraulic power transmission system for operating a press or the like the combination with a source of pressure fluid and a reversible fluid motor of a valve shiftable to forward and reverse positions to direct fluid to the motor in either direction and having a neutral position in which fluid is exhausted from one side of the motor, an electric operator for shifting said valve to forward position, an electric operator for shifting the valve to reverse position, means normally biasing the valve to neutral position, a threeposition, two-circuit holding relay for controlling the energization of each operator selectively, means for initially energizing said relay to start said motor forwardly, means for deenergizing said relay to start the motor reversely, and means operated by the platen for shifting said relay to a neutral position where both operators are deenergized to stop the motor.

5. In a hydraulic power transmission system for operating a press or the like the combination with a source of pressure fluid and a reversible fluid motor of a valve shiftable to forward and reverse positions to direct fluid to the motor in either direction and having a neutral position in which fluid is exhausted from one side of the motor, an electric operator for shifting said valve to forward position, an electric operator for shifting the valve to reverse position, means normally biasing -the valve to neutral position, a pair of electric circuits for controlling each operator separately, switch means in the first circuit for initiating and terminating energization of the first operator to cause the motor to move through a forward stroke and to stop, and switch means including a switch in the second circuit and responsive to pressure at said one side of the motor for controlling energization of the second operator and arranged to prevent initial energization thereof while the motor pressure is above a predetermined value.

6. In a hydraulic power transmission system for operating a press or the like the combination with a source of pressure fluid anda reversible fluid motor of a valve shiftable to forward and reverse positions to direct fluid to the motor in either direction and having a neutral position in which fluid is exhausted from one side of the motor, electric means for shifting said valve to reverse position, and a pressure responsive switch arranged in circuit with said means to prevent shifting of the valve to reverse position until the motor pressure effective during a forward stroke has fallen to a predetermined value.

FERRIS T. HARRINGTON. RALPH L. TWEE'DAL'E. 

